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Leak from nuclear waste site would be diluted: Experts

The “immense” waters of the Great Lakes will greatly dilute any radiation-bearing water that might leak from a proposed nuclear waste site on Lake Huron, says an expert group.

Fast-flowing surface water would also dilute leaking radiation, should the site be located in the ancient rock of the Canadian Shield, the group says.

A federal panel has asked an expert group of scientists to compare whether it would be better to inter nuclear waste at the actual Bruce site, or in ancient granite formations in the Canadian Shield.
TORONTO STAR/FILE PHOTO

The four-member group has filed a report with the federal panel examining Ontario Power Generation’s proposal to bury low- and intermediate-level nuclear waste in a limestone formation 680 metres below the surface, on the shore of Lake Huron.

The federal panel asked the expert group to compare whether it would be better to inter the waste at the Bruce site, or in ancient granite formations in the Canadian Shield.

The question of leakage from the site has heated up with the recent release of radiation from a nuclear waste site in New Mexico, the Waste Isolation Pilot Plant, or WIPP.

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The WIPP release does not appear to be related to water leakage — it followed an underground vehicle fire in February — but the fact that radiation had escaped at all prompted the federal panel to schedule additional hearings for the Bruce project.

At the WIPP site in New Mexico, work teams have re-entered the underground area, but are advancing in stages. They haven’t yet reached the area where the leak originated, and may not get there for days or weeks.

WIPP officials have drawn up an 11-stage scheme for drafting up a plan to re-open the site, and are only at the fourth stage.

At the Bruce site, the federal panel has been asking what happens if underground water is contaminated by radiation, and then leaks from the site.

The expert group’s report says that wherever the site is developed, any leaking water it will be significantly diluted.

The group says it’s possible that as much as 1,000 cubic metres a year of water contaminated with radiation might leak out of a site – although it rates the likelihood as “highly improbable.” (A thousand cubic meters is equal to a cube measuring 10 metres in each dimension.)

That’s a very small amount, the group says, given that the annual rainfall into Lake Huron is 42 billion cubic metres a year.

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And the volume of water already in the lake is 100 times more than the rainfall, or more than four trillion cubic metres.

As for a waste site in Canadian Shield granite, any leakage would flow into active streams and marshlands

“Hence, the volumes of the bodies of water available for dilution at the surface are either immense (Great Lakes) or actively flowing…so the dilution capacity is significant,” the experts conclude.

The dilution capacity for a site at the Bruce or in the Canadian Shield, the experts conclude, are “similar.”

But other characteristics of the two sites are not.

The expert group notes that granite is “naturally fractured,” and those cracks in the rock can transport radioactive material. That means a site in the Canadian Shield would require more “engineered barriers” to block the cracks.

The limestone at the Bruce site – which underlies a good chunk of rural Ontario – doesn’t have those fractures. It’s capped by a layer of shale that is also not liable to fracture.

Water can still seep through the limestone or shale, but the process is very, very slow in comparison with the rate at which is can travel through fractured granite, the expert group says.

“The Bruce DGR has a much lower probability of release of a significant concentration of radionuclides to the biosphere,” the group says.

(DGR, or deep geologic repository, is the technical term used to describe the proposed underground waste site.)

The expert group also notes that moving the waste from the Bruce site – where it has been stored on the surface for decades – to somewhere on the Canadian Shield would increase the risk of accidents during transport.

But both sites would be “well within the regulatory requirements for long term safety and environmental protection,” the expert group says.

The expert group isn’t the first to cast an approving eye at the geology of southern Ontario for storage of nuclear waste.

A separate process, run by the Nuclear Waste Management Organization (NWMO), is under way to find a location for a site to permanently bury high-level nuclear waste – which is used fuel.

(OPG’s proposed Bruce site won’t take used fuel. It will take low-level waste – such as used clothing and cleaning rags that remain radioactive for only a few hundred years. It will also hold and intermediate-level waste — including highly-radioactive components from reactor cores — which can remain dangerously radioactive for 100,000 years or more.)

The NWMO hasn’t yet identified a site, but is examining several options in the Bruce region, as well as in northern Ontario and Saskatchewan.

The NWMO issued a background paper in 2005 that specifically looked at the “Ordovician” shales and limestones – the formations containing the proposed OPG site.

“Based on current knowledge, there are a multitude of independent arguments suggesting that Ordovician shales and limestones occurring beneath southern Ontario provide a highly suitable environment to host a deep geological repository for spent fuel,” the paper concluded.

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